[SimplifyLibCalls] Transform log(exp2(y)) to y*log(2) under fast-math.

llvm-svn: 254317

1 files changed, 9 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index 47e587f..83afb1a 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -1322,6 +1322,15 @@ Value *LibCallSimplifier::optimizeLog(CallInst *CI, IRBuilder<> &B) {
     return B.CreateFMul(OpC->getArgOperand(1),
       EmitUnaryFloatFnCall(OpC->getOperand(0), Callee->getName(), B,
                            Callee->getAttributes()), "mul");
+
+  // log(exp2(y)) -> y*log(2)
+  if (F && Name == "log" && TLI->getLibFunc(F->getName(), Func) &&
+      TLI->has(Func) && Func == LibFunc::exp2)
+    return B.CreateFMul(
+        OpC->getArgOperand(0),
+        EmitUnaryFloatFnCall(ConstantFP::get(CI->getType(), 2.0),
+                             Callee->getName(), B, Callee->getAttributes()),
+        "logmul");
   return Ret;
 }
 
@@ -2301,7 +2310,6 @@ void LibCallSimplifier::replaceAllUsesWith(Instruction *I, Value *With) {
 // log, logf, logl:
 //   * log(exp(x))   -> x
 //   * log(exp(y))   -> y*log(e)
-//   * log(exp2(y))  -> y*log(2)
 //   * log(exp10(y)) -> y*log(10)
 //   * log(sqrt(x))  -> 0.5*log(x)
 //